Carbohydrates represent the largest fraction of biomass and various strategies for their efficient use as a feedstock for the preparation of commercial chemicals are being established. Biomass is of particular interest due to its potential for supplementing, and ultimately replacing, petroleum as a feedstock for such purposes. Carbohydrates obtainable from biomass comprise C2 to C6 sugars and are of particular interest industrially as they are a potential source of highly functionalised short chain carbon compounds.
This invention is directed towards the preparation of methionine α-hydroxy analogue and derivatives thereof from sugars in the presence of zeotype compounds. Methionine α-hydroxy analogue is 2-hydroxy-4-(methylthio) butanoic acid. Methionine α-hydroxy analogue and derivatives thereof may be used as a food/nutritional supplement in animal feed compositions/formulations.
It is known that C2-C6 sugars may be converted to methyl lactate and methyl vinylglycolate (MVG) in the presence of zeo-type materials such as Sn-BEA. EP 2 184 270 B1 and Science (2010) 328, pp 602-605 report average yields of methyl lactate of 64%, 43% and 44% at 160° C., in the presence of Sn-BEA and methanol from sucrose, glucose and fructose, respectively. Methyl vinylglycolate (MVG) is the major by-product with a reported yield of 3-11%. MVG may be produced in yields of up to 56% from the C4 sugar D-erythrose.
WO 98/32735 discloses a process for the preparation of methionine α-hydroxy analogue methyl ester, 2-hydroxy-4-(methylthio) butanoic acid methyl ester, in an 85% yield via a free radical addition of methylthiol to a non-conjugated olefinic substrate, i.e. methyl vinylglycolate (MVG). Although high yielding, radical reactions have the potential to form region-isomeric by-products.
WO 98/32735 also discloses an alternative, multi-step, commercially feasible process for preparing methionine α-hydroxy analogue, 2-hydroxy-4-(methylthio)butanoic acid. The process comprises a Michael addition of methyl mercaptan to acrolein (a conjugated olefinic substrate) in the presence of an organic amine catalyst to produce 3-(methylthio)-propanal, followed by nitrile addition and hydrolysis to the acid. Although the process is industrially feasible, the use of toxic and expensive reagents such as HCN and acrolein should be avoided.
ChemCatChem (2013) 5, pp 569-575 discloses the conversion of tetroses (C4 sugars) to MVG and MMHB under homogenous catalytic conditions. MMHB is selectively produced from erythrulose (C4 sugar) in the presence of a homogenous tin chloride catalyst.
Accordingly, it is desirable to provide an alternative process for the preparation of methionine α-hydroxy analogue and derivatives thereof. In particular, it is desirable to provide a process that is industrially feasible, it is therefore desirable that the process is high yielding, direct and selective. It is desirable that the process is carried out under conditions that are industrially feasible, with regents or catalysts that enable ease of production and reduced toxic waste, such as the use of heterogenous catalysts that may be regenerated. Additionally, the provision of a process wherein the substrates are derived from renewable sources such as C2-C6 sugars, is desirable. In particular because the sugar substrates are much less toxic and much cheaper than, for example acrolein and the HCN reagent, consequently the use of sugar substrates significantly lowers the costs of production.